In 1973, in preparation for my documentary, “Bolero,” I spent time observing the Los Angeles Philharmonic in rehearsal at the Hollywood Bowl. It was led by guest conductor James Levine, and featured Beverly Sills singing arias from Verdi's “La Traviata.” Levine, just twenty-nine years old, had already made a strong impression on the music world with his brilliant musicianship, his energy and self-confidence. He must have known that this concert with Beverly Sills was a kind of tryout for the next step up the ladder.

But things were not going well. In this pleasant outdoor theater, the orchestra had become too relaxed. They were not playing together, and Sills was unable to fit herself into their ragged rhythms. She kept looking to Levine for help, but though he was gesturing forcefully, he was unable to establish musical order. Realizing that a frustrated star soprano was not going to be good news for him, he put down his baton. Gradually the orchestra stopped, though a few straggling winds insisted on playing to the ends of their phrases.

“Ladies and gentlemen,” Levine said evenly. “You know and I know that this isn't working. Some of you are following me, more or less, some are following Beverly. I'll tell you what. Let's try it once with everyone following me, no matter what happens. If I can't keep you and Beverly together, let it be my fault. Let me be the one to blame.” The orchestra remained silent. Sills raised an eyebrow. Levine started again, and this time the orchestra stayed with him. If Sills changed the tempo in places, they continued to follow Levine and let him bring her along. The orchestra had accepted the presence of a professional on the podium.

This experience brought home to me again that to succeed, conductors need more than fine musicianship and a flawless ear. They must project a powerful aura of leadership, a sense of confident authority. Scherchen combined visionary ideas about music with a commanding presence. He persuaded orchestras to give him what he asked for, and they rewarded him with great performances.

Some conductors, after years of experience, become practical at solving problems. When I told Valery Gergiev I had always had trouble hearing the second wind players - flute, oboe, clarinet, and bassoon, he replied, “Why didn't you ask them to play louder?”

Ultimately, communication between conductor and orchestra must remain a mystery. Here's a statement from a 2009 interview with Robert Mann, the founding first violinist of the Juilliard String Quartet. He describes a period he spent in the violin section of the Cleveland Orchestra under George Szell.

“Certain conductors have an inner mixture of intuition and brain power. They can’t truly explain it in words, but they are somehow able to elicit from the least important person in the orchestra a sense of forward movement in the music, whether it be growing, or receding, or intensifying, or involving a certain kind of melodic nuance. They are able somehow, in their gestures, to translate that into something the musicians will understand and re-create in their playing. There are lots of conductors, but very few can really illuminate the score. George Szell was one of them.”

Szell was a great conductor, but he was also a practiced tyrant. It was said that he made a violinist return his new car and use the money to buy a better violin bow. Once, passing another musician on a stairway, Szell turned and said over his shoulder, “By the way, you’re fired.”

Today, with the growth of musicians' unions, conductors have learned to be more collaborative. Not too long ago, however, I witnessed an event that could have happened in the Szell era. During a rehearsal of a major American orchestra, one of the double bass players continued making the same mistake. The conductor left the podium, walked brusquely through the orchestra, past the horns and trombones, and stopped in front of one of the bass players. Shaking his finger at him, the conductor demanded to know why he could not play the passage correctly. The bass player had the sense not to say anything; he just stared back at the conductor. The orchestra looked grim; those near the awful scene turned away. When the conductor had expended his fury he returned to the podium and the rehearsal continued. It was clear that the maestro had forfeited whatever sense of common purpose he might have developed with the orchestra. Two years later, when his contract was up, he was gone.

Sometimes a conductor is so beloved that the musicians accept his uncontrollable demons. During a rehearsal, Arturo Toscanini was furious with a bassoonist, and began screaming at him in Italian. At the boiling point, Toscanini stormed off the podium and headed for the exit. As he reached the door the bassoonist yelled at him, “Fuck you, Maestro.” Toscanini shouted back, “It's too late to apologize,” and left.

Finally - a contrast in styles. Some years ago The Simon Bolivar Youth Orchestra from Venezuela played a program in Carnegie Hall, shared by the conductors Gustavo Dudamel and Simon Rattle. Dudamel, barely 30 years old, began with a performance of Bartók's “Concerto for Orchestra,” a virtuoso piece that shows off all the instruments in solos and in groups. Dudamel explored every facet of the music with a dynamism that was just short of wild. The young players were super-excited, almost swaying off their chairs. Under Dudamel the piece became a concerto for adrenaline. As the ending exploded in the hall, the audience was on its feet, shouting and clapping, overwhelmed by the student orchestra and its fiery young conductor.

After intermission Simon Rattle, Principal Conductor of the Berlin Philharmonic, came onstage to conduct the Shostakovich Symphony No. 10. Rattle, a tall man then in his mid-fifties, with a prominent mop of white hair, stood quietly on the podium. He looked around at the young players, establishing eye contact with each one of them. As he quietly raised his arms, the players put their instruments at ready, leaning slightly towards him. They shared a breathless moment of anticipation - we felt it in the hall - and Rattle started the symphony. He and the musicians, and the audience, dug into the music together.